1. Technical Field
The presently disclosed subject matter relates to an optical semiconductor device such as a light emitting diode and a photodiode, and a method for manufacturing the same.
2. Description of the Related Art
Conventionally, optical semiconductor devices such as described in Japanese Patent Application Laid-Open No. 2004-363454 have been known. FIGS. 1A, 1B, 1C, and 1D are views showing an example of the configuration of a conventional, typical optical semiconductor device. FIG. 1A is a trihedral drawing of the optical semiconductor device. FIG. 1B is a sectional view taken along line A-A of FIG. 1A. FIG. 1C is a sectional view taken along line B-B of FIG. 1A. FIG. 1D is a sectional view taken along line C-C of FIG. 1A.
With reference to FIGS. 1A, 1B, 1C, and 1D, this optical semiconductor device (for example, light emitting diode) is configured to include: an optical semiconductor chip 2 (such as an LED chip); a first lead 3; a second lead 104; a holder part 6 (also called a lamp house, a base part, a cover, etc.); a lens part 7; and a light-transmitting sealing material 8 (such as a light-transmitting soft sealing resin). The optical semiconductor chip 2 is mounted on the first lead 3. A wire 5 extends from the optical semiconductor chip 2 mounted on the first lead 3 and is connected (joined) to a second lead 104. The holder part 6 supports the first lead 3 and the second lead 104 at two locations, respectively. In this instance, a specific example of the wire 5 is a gold wire.
The first lead 3 has two terminals P1 and P2 which protrude outside and can be fixed by solder. The second lead 104 also has two terminals P3 and P4 which protrude outside and can be fixed by solder.
The holder part 6 has no bottom portion at its center area, or has a so-called frame shape. Namely, the holder part 6 has a space penetrating inside thereof. As a result, the first lead 3 and the second lead 104 are in contact with and supported by the holder part 6 only at two locations each (they penetrate the holder part 6). More specifically, since the holder part 6 has no bottom face thereinside, the first lead 3 and the second lead 104 are not in contact with the holder part 6 but are free in the inside space thereof (i.e., within an aperture framed by the holder part 6).
Now, when such an optical semiconductor device as shown in FIGS. 1A to 1D undergoes a thermal shock (i.e., a sudden temperature change from high to low temperature or a sudden temperature change from low to high temperature), the second lead 104 is likely to warp vertically, which may cause the wire 5 to break.
The reason for this is that the second lead 104 in the optical semiconductor device shown in FIGS. 1A to 1D is a single solid member. When the device is mounted on a mounting board, the two terminals P3 and P4 are fixed by solder or the like. Then, the second lead 104 warps vertically within the inside space of the holder part 6 with thermal expansion and/or thermal contraction of the mounting board when undergoing a thermal shock.
FIGS. 2 to 4 are diagrams for explaining the above described situation. When the second lead 104 warps vertically under a thermal shock as shown in FIG. 2, the wire (gold wire) 5 joined to the second lead 104 is also displaced vertically as shown in FIG. 3. The weakest portion of the wire 5 that is joined to the optical semiconductor chip 2 and the second lead 104 is the junction with the optical semiconductor chip 2. To be more specific, the junction with the optical semiconductor chip 2 is formed by recrystallizing the gold wire, followed by thermal and ultrasonic welding. This recrystallized portion has mechanical properties that are weaker than those of non-recrystallized portions. When the wire 5 is vertically displaced, the resulting vertical force therefore acts to stretch the recrystallized portion, whereby the recrystallized portion is thinned as shown in FIG. 4 with an increase in the possibility of a break of the wire 5.